– EARTHQUAKES –
Earthquakes are probably one of the most frightening and destructive happenings of nature that man experiences. The effects of an earthquake are often terrible. Earthquakes have caused the death of many human beings, much suffering, and great damage.
Today, the study of earthquakes has grown greatly as scientists all over the world study the causes of earthquakes. Scientists hope that their studies will improve the ways of predicting earthquakes and also develop ways to reduce their destructive effects. The scientific study of earthquakes is somewhat new.
Until the 18th century, few factual descriptions of earthquakes were recorded. In general, people did not understand the cause of earthquakes. Many believed that they were a punishment from God.
One early theory was that earthquakes were caused by air rushing out of caverns deep in the interior of the earth. On November 1, 1755, a serious earthquake occurred near Lisbon, Portugal. Shocks from the quake were felt in many parts of the world. After the quake, Portuguese priests were asked to observe the effects and to make written records. These records were the first scientific steps to write down the effects of an earthquake.
Since that time, detailed records have been kept of almost every major earthquake. Most earthquakes occur in areas around the Pacific Ocean. This belt of areas is called the ‘ring of fire’ and includes the Pacific coasts of North and South America, the Aleutian Islands, Japan, Southeast Asia, and Australia. Half a million people within the ‘ring of fire’ have died because of earthquakes and much valuable property has been severely damaged or destroyed.
An earthquake is the oscillatory, sometimes violent, movement of the earth’s surface that comes after a release of energy in the crust of the earth. Most destructive quakes are caused by the dislocation of the crust. Forces from beneath the surface of the earth cause the crust to bend and then break and the rocks on the surface move into a new position. The breaking of the rocks causes vibrations called ‘seismic waves’.
These vibrations travel from the source of the earthquake to distant places along the surface of the earth. The seismic waves cause the entire planet to tremble or ring like a bell. The vibrations produced by earthquakes are discovered, recorded, and measured by instruments called seismographs. Vibrations are of two general types: surface waves and body waves. Surface waves travel along the earth’s surface and body waves travel through the earth.
Surface waves usually have the strongest vibrations and probably cause most of the damage done by earthquakes. Currently, scientists are making studies to predict earthquakes. At the present time, scientists do not have the knowledge required to predict the time and size of earthquakes. However, a large group of scientists at the National Centre for Earthquake Research in California, has been able to predict the areas where earthquakes might occur. Research at the centre about the physical and chemical nature of rocks and their behaviour under the force of an earthquake will help engineers to design and build structure for areas that often suffer from 50 earthquakes.
A. Complete the following sentences.
1. Line 48, ‘their behaviour’ refers to the behaviour of .
2. The ‘ring of fire* is the belt of areas around the Pacific Ocean where
3. Seismographs the vibrations caused by earthquakes.
4 One characteristic of surface waves, which cause most of the damage done by earthquakes, is that they .
B. Mark the statements as True (T) or False (F).
1. Scientists hope to reduce the harmful effects of earthquakes by studying the nature.
2. Scientists at the National Centre for Earthquake Research in California can predict the time and size of earthquakes.
C. Mark the best choice.
1. Line 13, ‘caverns’ are probably .
a) earthquakes occurring in the interior of the earth
b)-strong winds caused by earthquakes
c) rivers and lakes in major earthquake areas
d) deep holes under the ground